Nanowires have the potential to revolutionize the technology around us. Measuring just 5 to 100 nanometers in diameter (a nanometer is a millionth of a millimeter), these tiny, needle-shaped crystalline structures can alter the way electricity or light passes through them.
They can emit, focus and absorb light and could therefore be used to add optical functionality to microchips. For example, they could generate lasers directly on silicon chips and integrate single-photon emitters for coding purposes. They could even be applied in solar panels to improve the conversion of solar radiation into electrical energy.
Until now, it was impossible to replicate the process of nanowire growth on silicon semiconductors – there was no way to repeatedly produce homogeneous nanowires in specific positions. Researchers from the Laboratory of Semiconductor Materials of EPFL, led by Anna Fontcuberta i Morral, in collaboration with colleagues from MIT and the IOFFE Institute, have developed a way to develop networks of nanowires in a highly controlled and reproducible manner. The key was to understand what happens at the beginning of nanowire growth, which runs counter to currently accepted theories. Their work has been published in Nature Communications.
"We believe this discovery will realistically integrate a series of nanowires on silicon substrates," says Fontcuberta i Morral. "Until now, these nanowires had to be grown individually and the process could not be replicated."
Get the right ratio
The standard process for producing nanowires is to drill tiny holes in silicon monoxide and fill them with a drop of liquid gallium. This substance then solidifies on contact with arsenic. But with this process, the substance tends to harden at the corners of the nano-holes, which means that the growth angle of the nanowires can not be predicted. We were looking for a way to produce homogenous nanowires and to control their position.
Research to control the production process tends to focus on the diameter of the hole, but this approach has not been successful. EPFL researchers have now shown that by modifying the diameter / height ratio of the hole, they can perfectly control the growth of nanowires. At the right ratio, the substance will solidify in a ring around the hole, which will prevent the nanowires from growing at a non-perpendicular angle. And the process of researchers should work for all types of nanowires.
"It's a bit like growing a plant, they need water and sunlight, but you have to get the right quantities," says Fontcuberta i Morral.
This new production technique will be a boon for research on nanowires and other samples should soon be developed.
Nanowires have the power to revolutionize solar energy (with video)
J. Vukajlovic-Plestina et al. Fundamental aspects for the localization of silicon-catalyzed III-V nanowires Nature Communications (2019). DOI: 10.1038 / s41467-019-08807-9